1. Field of the Invention
This invention relates to an intermediate amplifier for a transmission system intended for communications transmission applications using light waves in optical wave guides, and more particularly to such an amplifier which includes an optical amplifier for amplifying the light waves on the laser principle and to filtering techniques for restricting the frequency band of the amplifier to the frequency band of the pulses being transmitted.
2. Description of the Prior Art
In the German published application 21 41 842 an optical intermediate amplifier operating as a laser amplifier is disclosed, in which amplifier the light signals are amplified in a doped semiconductor monocrystal which functions as the active medium. In one embodiment of that invention (FIG. 1), the optical amplifier utilizes a doped single crystal semiconductor 7 which is electrically pumped by way of the elements 11 and 12 and which is disposed between and coupled to the ends of a pair of light conductors 3 and 4 by way of output couplings thereto. If desired, the end surfaces 13 and 14 (FIG. 2) of the semiconductor laser are inclined toward each other to reduce undesirable oscillations in the semiconductor material. Another embodiment of the invention (see FIG. 3) finds the amplifying material, such as a semiconductor laser 7, provided with resonator mirrors 15 and 16 which reflect the amplified light signals several times to obtain the desired mode in the amplified light signals which are then directed back to the same semiconductor 3 and subsequently separated therefrom by branching to a separate conductor. In another embodiment (FIG. 4), the material forming the laser amplifier is provided with mirrors 15 and 16 which are arranged to produce a zig-zag path through the amplifying material 7 for exit in a separate conductor 4 in a direction which is opposite to the direction of incidence wave guide 3. In still another embodiment of the invention (see FIG. 5) an optical active material 18 of a solid state laser is carried on a portion 17 of a circumferential shell 6 of a light conductor 3 and optically pumps the active material 18 to amplify surface waves in the shell 6 to obtain the amplifier signal for the information transmission system. Each embodiment is preferably formed with the wave conductor 3 through the utilization of integrated techniques.